Compensated strain gauge



Dec.7,1943. A SHAYNE ETAL 2,336,371

COMPENSATED STRAIN GAUGE Filed Feb. 24, 1940 2 Sheets-Sheet l FYiZHWENTORS ALfiXANDER SHAY/V5 I g m/N0 A. W/ gH/VS Dec. 7, 1943.

A. SHAYNE ET AL COMPENSATED STRAIN GAUGE Filed Feb. 24, 1940 I I AL 2.Sheets-Sheet 2 gym 0A. w/ru/m/a r ATTORNEY Patented Dec. 7,

UNITED STATES "PATENT OFFlCE zssasn coMrENsA'rEn s'raAm GAUGEApplication February 24,1940, Serial No. 320,668

' Claims. (01. 265-1) This invention relates to strain gauges and inparticular to strain gauges as used on rolling mills to indicate andrecord the bearing load pressures encountered and also in order to levelthe rolls with respect to eachother soas to insure uniform thickness ofthe bar or sheet pass- Products, Inc., a corpotemperature changes ofindividual parts occur on both sides of the symmetric center line anding therethrough. One such strain gauge is described in our joint patentapplication, Ser. No. 294,154, filed September 9, 1939, of which thispatent application is a continuation in part. In said prior applicationit was explained that due to the changes in temperature encounteredespecially on hot strip rolling mills, it is necessary to providespecial automatic means for compensating the instruments for changes dueto changes of temperature. automatic temperature compensation willeliminate the effect of temperature changes upon the indicator orrecorder readings, if suflicient time between working periods is allowedfor the temperature compensator to do its work. In certain cases,however, it may be necessary to operate without the benefit of theautomatic temperature compensator. Then it is impossible to eliminateeffects due to temperature changes on the readings of the instrmnentduring the whole period the compensator is not used. It therefore isquite possible that the indications are inaccurate for at least part ofthe working cycle.

The present invention is for the purpose of overcoming thisdisadvantage. Experiments have shown that by. far the greatest part ofeffects due to temperature change occur on that part of the strain gaugeequipment which is mounted on the rolling mill bearing frame. Waterfiows over this frame from the point where it is applied to cool therolls, and tends to cool the lower part of the frame more than the upperpart. The upper part of the frame and the rolls absorb heat from the hotstrip passing through the mill and this heat travels'through the solidframe tending to gradually increase the temperature of the lower arch,at which point we prefer to mount our primary electro-magnetic gaugeunit. If the water flow is stopped, for a time, such as when the mill isidle, the lower arch will heat up faster than during working periodswhen the cooling water tends to keep the temperature of the arch down.Therefore, it is obvious that marked fluctuations of temperature dooccur in the vicinity of the place where the gauge unit is mounted.

One of the objects of the invention is to obtain a design for the gaugeand its actuating members which is symmetrical throughout so thatExperience has shown that thereby cancel each other.

Another object of the invention is to provide a connection between thegauge and its actuating arm which is rigid in the direction in which thegauge measures and which is substantially free and resilient in a planeperpendicular to that direction.

A further object of the invention is to improve the individualelectro-magnetic gauge unit to such an extent that it becomes fullybalanced against changes in temperature, voltage and frequency.

In order to explain the several features of our invention, reference ismade to the accompanying drawings.

Fig. 1 is a front elevation of a bearing frame 01' a l-high" rollingmill.

Fig. 2 is a front elevation of the gauge part and its actuating arm on alarger scale.

Fig. 3 is a bottom view of the same instrument.

Fig. 4 is an elevation of another type of electromagnetic gauge.

Fig. 5 shows the instrument of Fig. 4 in a bottom view.

Fig. 6 is a section on line 6--6 of Fig. 4.

Fig. 7 shows a further modification.

Referring to Fig. 1, one of the bearing frames of a 4-high" mill isshown at I. Inside of this bearing frame are located the bearing chocks'l and ID for the back-up rolls 4 and 5, which enclose the bearinghousings 8 and 9 for the work rolls 2 and 3. The work rolls 2 and 3 areof comparatively'small diameter and are driven by a powerful motor notshown. The back-up rolls 4 and 5 are of large diameter and serve thepurpose of preventing excessive deflections of the work rolls while thebar is passing through. Pressure is applied to the rolls by means of amotor driven screw 6 which contacts the bearing chock I of the upperback-up roll. The pressure is now transmitted through this roll to thework rolls and from there through the second or lower back-up roll tothe lower part of the frame I. The lower arch ll of the frame thereforeis subjected to bending stresses. A second frame identical to the frameI carries the second set of bearings for the rolls and is subjected tosimilar forces by another screw which is coupled to the screw 6.

It is evident that if both screws are rotated so that they advance in adownward direction, pressure will be applied between all rolls and willresult in elastic deformation of all parts of the machine. The verticalmembers l2 and I2 of the frame will stretch when load is applied whilethe lower arch II and the upper arch l3 will bend, and to some extentalso stretch. At the lowest part of the lower arch N, we prefer to mountour micrometer equipment within a box II. The magnetic micrometer unititself is shown at l5. The actuating arm I6 is welded to a block I!which in turn is welded directly to the steel frame. As has been shownin the above mentioned prior application, this arrangement results inconsiderable mechanical amplification of the bending deflection which isapplied to the gauge l5. 1 V

Fig. 2 shows in an elevation view more in detail the parts l5, I6 and llof the gauge unit and arm. A block I8 is welded to the lower arch andcarries a pin I! to which by means of a clamp 20 the frame 2| of adifferential transformer micrometer is attached, which may be of thesame design as'described in detail in our above mentioned priorapplication. A primary coil 22 surrounding the center leg of athreelegged frame 2| is excited from an. alternating current source andinduces in the secondary coils 23 and 24 potentials which aresubstantially equal and opposite as long as the armature 25 which ispivoted by means of a torsion wire 26, is in its neutral position sothat at 21 and 28 equal air gaps exist. The wire projects from the sidesof armature 25 (see Fig. 3) and is clamped against movement, as shown,in the fixed posts projectting from the micrometer frame 2 l.

Attached to the armature at its center point is a split block 28provided with a clamping screw 30. Through the slot which splits thisblock passes a steel wire 3| which is firmly held in place by twoadjustable screws 32 and 33. shown in Fig. 3. these screws are held in aU- shaped frame 34, the two legs of which are split by slots 35 to allowclamping of the screws 32 wire will occur with equal magnitude on bothsides of the center line, thereby cancelling their effects upon thearmature position.

Any bending of the frame, however, in the lane of the paper of Fig. 2will tend to rotate bly therefore will respond only to motions in theand 33 by means of clamping screws 36 and 31.

The nuts 38 and 39 serve the purpose of tightening the wire 3| to itsinitial working tension which preferably is kept low, around 1,000 to2,000

lbs. per sq. in. They also allow shifting of the wire lengthwise toadjust the armature position.

The frame 34 in turn is fitted to an arm l6 by means of a keyway and isheld centrally and symmetrically to this arm by means of bolt 4|. Thearm IS in turn is welded to a block I! which is welded to the lower archll of the bearing frame.

The connection between the arm l6 and the gauge unit is accomplished byclamping the wire 3| by means of screw 30 to the split block 29. As thisclamp is located also on the longitudinal center line of the arm and themicrometer frame 2 I, the whole assembly is substantially symmetrical.Any change of temperature within the box ll which surrounds the wholeassembly will equally affect all parts of the gauge and of the arm.Temperature changes causing increase or decrease of any dimensionparallel to the longitudinal center line of the assembly will cause theends of the wire 3| to bend equally and oppositely around pivot 26 inthe plane of the paper so that such changes will have no influence uponthe position of the armature 28. Therefore such changes cannot appear inthe indications of the instrument, which was fully described in ouraforementioned prior application, because the dials and indicators inthe device will not move. Due to the symmetry of the assembly, changesdue to temperature in a direction parallel to the direction of thelongitudinal axis of wire 3| but not to any motion perpendicularthereto. If, therefore, under the influence of working force ortemperature, the frame stretches or warps resulting in relative motionbetween the arm I 6 and the micrometer in the direction of theirlongitudinal center line, such stretching or warping will not berecorded by the instrument.

Figs. 4, 5, and 6 show a similar arrangement of arm and micrometer butwith a modified form of connection to the deflecting arm. In this case,the clamp which holds the wire is attached to the arm 58 and the wire 58is attached to the micrometer. The armature consists of an arm 5|connected by a core 52 to a second arm 53 forming the letter H. The arm5| carries two clamps 54 and 55, formed by blocks of steel split in themiddle and capable of being clamped together by means of clamping screws56 and 51. A wire 58 is stretched taut between the two clamps and heldin position by tightening the clamping screws 56 and 51.

The arm 59 which performs the same function as arm 16 described in Figs.2 and 3 is fastened to a block 60 which is welded to a plate 6|. Thisplate in turn is welded to the frame ll of the rolling mill housing. Theplate 6| and the plate 62 carrying the micrometer unit are preferablycut apart at 63 after the plate, or preferably only the extreme ends ofthe plate 6l-62 are welded to the arch. The cut 63 is made in order toallow unrestricted movement of the parts SI and 62 under stress.

The free end of arm 59 carries in a hole a screw stud 64 which isthreaded over its whole length. In order to be able to clamp this screwstud which can slide back and forth in the hole, the end of the arm isslotted as shown at 65 and is provided with 'two clamping screws 66. Aworm wheel 61 is threaded on the inside and serves as a nut for thescrew stud 64. Said wheel is turned by a worm 68, the shaft 69 of whichextends outwardly and has a slot so that it may be turned by means of ascrew driver. The screw stud 64 is prevented from turning after it hasbeen adjusted, by a pin 10 which slides in the slot 65. A two-part clampfits with one end over the screw stud 64 and at the other end clampsacross the wire 58, and if tightened up forms a rigid connection betweenthe screw stud 64 and the wire 58.

Initial adjustment of the assembly which is performed in Fig. 2 by meansof the two nuts 38 and 39 is accomplished in Figs. 4 and 5 by means ofthe worm 68. Turning this worm rotates the worm wheel 61 and therebymoves the stud 66 lengthwise.

The action of this assembly is substantially identical with that ofFigs. 2 and 3 inasmuch as it allows substantial freedom for any motionperpendicular to the longitudinal axis of the wire 58 but will result intilting of the arm 5| if a motion occurs in the direction of this axis.The arms 5| and 53 are connected by the core member 82 which carries thecoil 13. As 'shownin Fig." 6, the arms II' and" are attached to oppositesides of the core 82 and are notched, so as to form narrow air gaps14,15, '18 andII-with pole pieces 18 and 19. These pole'pieces in turnare carried on cores 88 and 8| which are screwed to a yoke 82. The cores80 and 8| each may carry a coil winding 84 and 83, The armature core 52is pivoted by means of two torsion wires 85 and 88 which are clamped totwo legs 81 and 88.

Either the coil 13 or the two coils 83 and 84 may be employed as primarywinding. If it is assumed that 13 is the primary winding the flux willextend only through the arm 53, the pole pieces 18 and 18, returningthrough the arm Provided the four air gaps 14-11 are equal, all fourgaps will pass an equal amount of magnetic flux. If, however, thearmature assembly consisting of the core 52 with its two arms 5| and 53is tilted so that air gaps 18 an; 14 are reduced while air gaps I5 and11 are increased, then some of the flux will pass through core 80, yoke82 and core 8|. Tilting of the armature in opposite directionwillreverse this secondary fiux. If the coils 83 and 84 are now connected inseries so that their induced voltages add up, they will show potentialsproportional as to sign and amplitude to the movement of the armaturearound its pivot 86.

Inasmuch as it is extremely difilcult to produce arrangements inmagnetic circuits in such a way that perfect symmetry prevails, it is tobe expected that unequal stray flux will have an eflfect upon thevoltage of coils 83 and 84. In other words, the potentials in thesecoils may be slightly out of phase with each other, thereby preventingthe total secondary voltage from showing perfect zero at the time thearmature moves through its neutral position. This condition may beremedied easily by magnetic shunts as shown at 88. By varying theposition and the size of this shunt, it is possible to balance the strayflux to obtain substantially perfect zero condition of the micrometer.The closer element 90 is positioned to member 81 the less of the strayflux will be concentrated in bar 82 and the less will be directedthrough coil 84. The closer element 88 is moved to coil 84, the morestray flux it will concentrate in the latter coil. Element 90 may heslid in a keyway in bar 82 and locked in position by the screw shown.

Another preferred way of obtaining such balance is shown in Fig. '7. Thetwo coils 83 and 84 have been eliminated and are replaced by a coil 9|which is placed substantially in the center of the yoke 82'. Twoadjusting screws 92 and 93 are threaded into the cores 80 and 8! andserve the purpose of shifting the coil 9| until perfect zero of themicrometer is obtained. By shifting the coil, the influence of the twostray fields of the gauge can be fully equalized in their effects uponthe coil 9|.

The advantage of the micrometer as shown in Figs. 4, 5, 6 and 7 comparedwith the micrometer as shown in Figs. 2 and 3 is that only thedifferential flux fiows through the secondary coils, whereas the gaugeas shown in Fig. 2 carries the full amount of flux through the coils. Itis also quite evident that it is much easier to balance the gauge asshown in Fig. '7 as compared with the one shown in Fig. 2. Perfectbalance of the gauge results in increased stability under changes ofvoltage and frequency when the micrometer works together with theassociated apparatus of the strain lndicator as described in our prior mic ti 1 It is obvious that in the gauge as shown in Figs. '4-"7, primaryand secondary coils may b3 reversed. The exciting'current may be appliedtoco'ils 88 and. 84 or"to coilal. In that case the coil 13 becomes asecondary coil.

As many changes could be made inthe above construction and manyapparently widely diflerent embodiments of this inventioncould be madewithout departing from the scope thereoflit is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limp-ing sense.

. Having described our invention, what we claim and desire to secure byLetters Patent is:

1. In a temperature compensated strain gauge or the like for measuringone component only of the strain in a part under stress with respect toanother part, a wire extending in the direction of the component strainto be measured, means for connecting spaced points on said wire to oneof said parts and placing it under moderate tension, and means forconnecting a mid-point on said wire to the other of said parts, saidlastnamed means including a relative motion detecting and measuringdevice responsive to the relative movement of said two means forindicating the strain.

2. In a device for measuring the bending deflection of a member underload, an actuating and amplifying arm attached with one end to a pointon said member, an electromagnetic micrometer attached to another pointof said member adjacent to the other end of said arm and placedsymmetrically with respect to the longitudinal center line of said arm,a wire under tension suspended across the movable part of saidmicrometer and carried thereby laterally with respect to said centerline, a clamp mounted at the last named end of said arm adapted toconnect the center of said arm. to-the center of said wire wherebymovements of said arm due to bending of said member are transmittedfully to said micrometer, while movements due to stretch of said memberand due to temperature changes as well as all other movements ,in aplane normal to said wire'are prevented from affecting the micrometer.

3. A temperature compensated strain gauge as claimed in claim 1 whereinsaid motion detecting and measuring device comprises a pivoted armaturewhich is rocked by said motion, and inductive windings adjacent thereto,the output of which is varied by the rocking of said armature.

4. In a strain gauge or the like for measuring one component only of thestrain in a part under stress with respect to another part, an elongatedstrain responsive means fixed at one, end to said first part with itsfree end movable angularly in response to the component strain to bemeasured, a motion detecting and measuring device mounted on the otherof said parts collinear and adjacent the free end of said responsivemeans, means connecting the free end of said responsive means to saiddevice, said connecting means including a filament anchored at spacedpoints to said responsive means and substantially rigid along itslongitudinal axis and yielding about axes normal to said-longitudinalaxis, said responsive means being positioned so that movements thereofin the direction of the component strain to be measfilament, V c

5. In astrain gauge or the like for measuring one component only of thestrain in a part under stress with respect to another part, strainresponsive means connected to said first part and movable in thedirection of the component strain to be measured, a motion detecting andmeasuring device mounted on the other of said parts, means connectingsaid responsive means to said device, said connecting means including aflla- 2,ssc,a71 ured are parallel to the longitudinal axis of said

